It sounds as if you're purchasing a raw food? True raw is really best, but if you're using something like Nature's Variety that's quite good as well.

The reason this is true is because cats are obligate carnivores. That means they are designed to and are required to eat diets high in meat-based proteins. Also high in fat, but not as high as the protein. Any grains they ingest are minor, few and far between – anything that might be found in a mouse's stomach, but they are not necessary.

In other words, the mouse is the perfect food for cats, and the raw diet attempts to recreate that by providing meat, organs and bones.

I've collected a lot of articles that will tell you the same thing in much more detail – but still easy to process.

You can learn more too by joining any or all of the raw food groups on Yahoo.

EDIT: Cats don't eat raw meat in the wild because they don't know how to cook as someone suggested. I've never heard anything so silly! Cats' digestive tracts are much shorter than humans. This is why they're able to eat raw meat and not suffer from the same bacteria humans would if they did the same. That doesn't mean your cat can eat rotten meat – you still want to take care with it – but it's much safer for them.

http://www.catchow.com/home_milestones_kc.aspx

Good luck!